1. Field of the Invention
The present invention relates to a webbing retractor which, at the time a vehicle rapidly decelerates and by using a locking device, temporarily locks rotation in a webbing pull-out direction of a spool on which a webbing for restraining a vehicle occupant is taken-up in a roll form by urging force, and which, in this state, permits a predetermined amount of rotation of the spool in the webbing pull-out direction due to load of a predetermined value or more being applied from the vehicle occupant to the webbing.
2. Description of the Related Art
Generally, a three-point-type seat belt device is structured so as to include a webbing for restraining a vehicle occupant, an anchor plate, a webbing retractor, a shoulder anchor, a tongue plate, and a buckle device. The anchor plate fixes one end portion of the webbing to the floor of the vehicle. The webbing retractor is a device which is disposed at the lower end portion of the center pillar of the vehicle and which takes-up the other end portion of the webbing in a roll form by urging force. The shoulder anchor is disposed at the upper portion of the center pillar, and an intermediate portion of the webbing is movably inserted through the shoulder anchor. An intermediate portion of the webbing passes through the tongue plate. The buckle device stands upright at the side of a seat of the vehicle, and the tongue plate engages therewith.
Various types of the above-described webbing retractor have been proposed. In one type, when the vehicle rapidly decelerates, the webbing retractor temporarily stops rotation of the spool in the webbing pull-out direction. Thereafter, due to a load of a predetermined value or more being applied to the webbing from the vehicle occupant, a torsion bar, which is provided integrally with and coaxially with the axially central portion of the spool, is twisted. The spool is thereby rotated by a predetermined amount in the webbing pull-out direction. In this way, the load which the vehicle occupant receives from the webbing which is in a locked state can be lessened. This mechanism is called a xe2x80x9cforce limiter mechanismxe2x80x9d.
Recently, structures have been proposed in which the load, at the time when the spool can rotate again by a predetermined amount in the webbing pull-out direction due to an increase in the webbing tensile force after the rotation of the spool in the webbing pull-out direction has been stopped at the time when the vehicle rapidly decelerates (this load is the force limiter load and hereinafter will be abbreviated as xe2x80x9cFL loadxe2x80x9d), is set to be two stages. Namely, in the initial stage of rapid deceleration of the vehicle, the FL load is maintained high, and the energy absorption efficiency is high. Thereafter, by reducing the FL load, the load which the vehicle occupant receives from the webbing is reduced. There are several concrete means for realizing such operation. One is a method in which a wire is made to span between the spool and the locking device in advance. The wire is usually held in an installed state. When the force limiter mechanism operates, the wire, whose base end portion is fixed to a push nut formed at the locking device, is pulled out from the spool while being strongly rubbed, and the wire is thereby made to bear the additional amount of the FL load.
However, if the above-described structure in which the wire is strongly rubbed is utilized, the following problems arise. Employment of this structure is based on the premise that the base end portion of the wire is reliably fixed to the locking device. In conventional techniques in which the base end portion of the wire is press-fit into the push nut, it is difficult to ensure a strongly fixed state. Moreover, when rattling arises in a case in which the base end portion of the wire is fixed to the push nut, noise may be generated.
In view of the aforementioned, an object of the present invention is to provide a webbing retractor which can reliably fix the base end portion of an elongated resistance imparting member to a locking device, and which can prevent the generation of noise.
An aspect of the present invention is a webbing retractor comprising a spool taking up a webbing, for restraining a vehicle occupant, in a roll form by urging force; an energy absorbing member connected coaxially to the spool; a locking device stopping rotation of the energy absorbing member in a webbing pull-out direction, at a time of rapid deceleration of a vehicle; a resistance imparting member whose one end portion is fixed to the locking device and another portion of which is anchored at the spool; and a push nut formed at a portion of the locking device. The energy absorbing member usually rotates integrally with the spool. In a state in which rotation of the energy absorbing member in the webbing pull-out direction is impeded, the energy absorbing member deforms due to load of a predetermined value or more being applied to the energy absorbing member via the spool, and permits a predetermined amount of rotation of the spool in the webbing pull-out direction. The resistance imparting member has a concave groove in an outer peripheral surface of the one end portion. The resistance imparting member usually rotates integrally with the spool without imparting rotational resistance to the spool. After locking by the locking device, in an initial stage of a state in which the spool rotates in the webbing pull-out direction, the resistance imparting member imparts resistance to the rotation of the spool in the webbing pull-out direction, and thereafter, separates from the spool and cancels the state of imparting resistance. The push nut has a plurality of engagement pieces. A length of one or more the engagement pieces is substantially longer than a length of the other engagement pieces. When the push nut is pressed-in, the plurality of engagement pieces substantially deform and engage with the concave groove of the resistance imparting member.
In accordance with the present invention, the energy absorbing member, which is coaxially connected to the spool, usually rotates integrally with the spool in the webbing pull-out direction and the webbing take-up direction.
When the vehicle rapidly decelerates, rotation of the energy absorbing member in the webbing pull-out direction is stopped by the locking device. In this way, the rotation of the spool in the webbing pull-out direction also is temporarily stopped. However, inertial force toward the front of the vehicle is applied to the vehicle occupant. Accordingly, because load in the pulling-out direction is applied to the webbing from the vehicle occupant, when this load reaches a predetermined value or more, the energy absorbing member deforms and the spool is rotated by a predetermined amount in the webbing pull-out direction. As a result, the load applied from the webbing to the vehicle occupant is reduced.
In the present invention, the one end portion of the elongated resistance imparting member is connected to the locking device, and the other end portion is anchored at the spool. Therefore, the resistance imparting member usually rotates integrally with the spool without imparting rotational resistance to the spool. When the vehicle rapidly decelerates, in the initial period of the stage in which the rotation of the energy absorbing member in the webbing pull-out direction is locked by the locking device, the resistance imparting member imparts resistance to the rotation of the spool in the webbing pull-out direction. Accordingly, in the initial stage of rapid deceleration of the vehicle, energy is absorbed at an FL load, in which are added together both an FL load due to deformation of the energy absorbing member and an FL load due to the rotational resistance which the resistance imparting member imparts to the spool. Thereafter, because the resistance imparting member separates from the spool, the state in which the resistance imparting member imparts resistance to the spool is cancelled. Thus, after the initial stage of the rapid deceleration of the vehicle, energy is absorbed at the FL load due to the deformation of the energy absorbing member. In this way, in accordance with the present invention, the FL load is set to be two stages. At the initial stage of the rapid deceleration of the vehicle, the energy absorption amount is large, and the amount by which the webbing is pulled out (the amount of movement of the vehicle occupant toward the front of the vehicle) is suppressed. Thereafter, the energy absorption amount is decreased and the load applied to the vehicle occupant is lessened.
Moreover, in accordance with the present invention, the concave groove is provided in the outer peripheral surface of the one end portion of the resistance imparting member, and the push nut is provided at the locking device. The push nut is formed from a plurality of engagement pieces which, due to the operation of pressing-in the one end portion of the resistance imparting member, deform and engage with the concave groove. Therefore, the one end portion of the resistance imparting member can be reliably fixed at the locking device.
In addition, in accordance with the present invention, the length of one or more of the engagement pieces is longer than the length of the other engagement pieces. Therefore, the one end portion of the resistance imparting member can be reliably pushed toward the other engagement pieces by the one or more engagement pieces. Accordingly, it is possible to prevent rattling between the one end portion of the resistance imparting member and the push nut of the locking device.